This invention relates to novel lightweight construction materials possessing excellent properties.
Foamed polyethylene and polystyrene are suitable materials for shaping and are widely used as construction materials, furniture materials and packaging materials. On the other hand, sheets of plastics such as polyethylene and polystyrene processed to have complementary concavoconvex patterns on their both surfaces by means of press molding are widely used as buffering material.
However, materials having complementary concavoconvex patterns on both surface thereof (referred to hereinafter simply as materials having a core structure) have not yet been manufactured by press molding from foamed polyethylene or polystyrene sheets. This is ascribable to the reason that foamed plastics are poor in moldability and difficult to form the core structure therein, and even if the core structure were formed, the resulting material would not be processed to articles for practical use because of their high heat shrinking percentage and low moisture permeability.
As the results of many researches made for obtaining practically utilizable material having a core structure from foamed plastics, it has now been formed unexpectedly that a polyethylene type resin containing a relatively large amount of an inorganic calcic filler is excellent in moldability and is easily processed to have the core structure and that the resulting articles are low in heat shrinking percentage and high in moisture permeability. This invention has been accomplished on the basis of the above finding.